Impact of Endorectal Balloon in the Dosimetry of Prostate and Surrounding Tissues in Prostate Cancer Patients Treated with IMRT

The dosimetric effect of endorectal balloon repositioning or failure was assessed in 10 prostate cancer patients treated with intensity modulated radiation therapy (IMRT). Three extreme clinical scenarios were simulated by placing the balloon in the most superior and inferior positions within the rectum and by removing the balloon. Treatment planning was performed by obtaining a computed tomography (CT) image with the balloon in the most superior position (plan 1). Subsequently, the isodose lines of plan 1 were superpositioned over the anatomy of 2 other CTs, one obtained with the balloon in the most inferior position and another without the balloon (plans 2 and 3, respectively). Dose-volume histograms (DVHs) of the prostate and surrounding tissues were generated and compared for all 3 plans. The prescribed radiation dose to the prostate and seminal vesicles was 70 Gy in 35 fractions. Balloon repositioning resulted in significant changes only for the seminal vesicles, where the minimum doses decreased from 70.39 to 61.58 Gy, and the percent volume below 70 Gy increased from 1.62% to 8.39%. Balloon failure resulted in significant decreases in mean and minimum doses for prostate from 74.36 to 72.84 Gy and 67.62 to 50.96 Gy, respectively. Similar decreases in the mean and minimum doses were also observed for seminal vesicles from 74.21 to 64.43 Gy and 70.39 to 41.74 Gy, respectively. Balloon repositioning did not affect normal tissue doses, while balloon failure significantly decreased the upper rectum mean doses from 30.79 to 19.38 Gy. This study demonstrates that repositioning of the endorectal balloon results in increased dose inhomogeneity for seminal vesicles, while balloon failure causes significant prostate and seminal vesicle underdosing without overdosing normal tissues.     

Impact of Endorectal Balloon in the Dosimetry of Prostate and Surrounding Tissues in Prostate Cancer Patients Treated with IMRT

The dosimetric effect of endorectal balloon repositioning or failure was assessed in 10 prostate cancer patients treated with intensity modulated radiation therapy (IMRT). Three extreme clinical scenarios were simulated by placing the balloon in the most superior and inferior positions within the rectum and by removing the balloon. Treatment planning was performed by obtaining a computed tomography (CT) image with the balloon in the most superior position (plan 1). Subsequently, the isodose lines of plan 1 were superpositioned over the anatomy of 2 other CTs, one obtained with the balloon in the most inferior position and another without the balloon (plans 2 and 3, respectively). Dose-volume histograms (DVHs) of the prostate and surrounding tissues were generated and compared for all 3 plans. The prescribed radiation dose to the prostate and seminal vesicles was 70 Gy in 35 fractions. Balloon repositioning resulted in significant changes only for the seminal vesicles, where the minimum doses decreased from 70.39 to 61.58 Gy, and the percent volume below 70 Gy increased from 1.62% to 8.39%. Balloon failure resulted in significant decreases in mean and minimum doses for prostate from 74.36 to 72.84 Gy and 67.62 to 50.96 Gy, respectively. Similar decreases in the mean and minimum doses were also observed for seminal vesicles from 74.21 to 64.43 Gy and 70.39 to 41.74 Gy, respectively. Balloon repositioning did not affect normal tissue doses, while balloon failure significantly decreased the upper rectum mean doses from 30.79 to 19.38 Gy. This study demonstrates that repositioning of the endorectal balloon results in increased dose inhomogeneity for seminal vesicles, while balloon failure causes significant prostate and seminal vesicle underdosing without overdosing normal tissues.     

Sparing of the penile bulb and proximal penile structures with intensity-modulated radiation therapy for prostate cancer

Quality of life is an important consideration in the treatment of early prostate cancer. Laboratory and clinical data suggest that higher radiation doses delivered to the bulb of penis and proximal penile structures correlates with higher rates of post-radiation impotence. The goal of this investigation was to determine if intensity-modulated radiation therapy (IMRT) spares dose to the penile bulb while maintaining coverage of the prostate. 10 consecutive patients with clinically organ confined prostate cancer were planned with 3D conformal radiation therapy (3D-CRT) or IMRT to give a dose of 74 Gy without specifically constraining the plans to spare the penile bulb. All 10 patients were ultimately treated with IMRT. Dose-volume histograms were evaluated and the doses to prostate, rectum, bladder and penile bulb were compared. IMRT reduced the mean penile bulb doses compared with 3D-CRT (33.2 Gy vs 48.9 Gy, p<0.001), the percentage of penile bulb receiving over 40 Gy (37.7% vs 67.2%, p<0.001) and the dose received by >95% of penile bulb (5.3 Gy vs 11.7 Gy, p=0.003). Maximum penile bulb doses were higher with IMRT (81.2 Gy vs 73.1 Gy, p<0.001) although the volume of this high dose region was small. Both methods resulted in similar coverage of the prostate. The volume of rectum receiving 70 Gy was significantly reduced with IMRT (18.4% vs 21.9%, p=0.003) but the volumes of bladder receiving 70 Gy were similar (p=0.3). IMRT may potentially reduce long term sexual morbidity by reducing the dose to the majority of the penile bulb.     

Development of a simultaneous boost IMRT class solution for a hypofractionated prostate cancer protocol

The purpose of this work was to develop a robust technique for planning intensity-modulated radiation therapy (IMRT) for prostate cancer patients who are to be entered into a proposed hypofractionated dose escalation study. In this study the dose escalation will be restricted to the prostate alone, which may be regarded as a concurrent boost volume within the overall planning target volume (PTV). The dose to the prostate itself is to be delivered in 3 Gy fractions, and for this phase of the study the total prostate dose will be 57 Gy in 19 fractions, with 50 Gy prescribed to the rest of the PTV. If acute toxicity results are acceptable, the next phase will escalate doses to 60 Gy in 20 x 3 Gy fractions. There will be 30 patients in each arm. This work describes the class solution which was developed to create IMRT plans for this study, and which enabled the same set of inverse planning parameters to be used during optimization for every patient with minimal planner intervention. The resulting dose distributions were compared with those that would be achieved from a 3D conformal radiotherapy (3DCRT) technique that used a multileaf collimator (MLC) but no intensity modulation to treat the PTV, followed by a sequential boost to raise the prostate to 57 Gy. The two methods were tested on anatomical data sets for a series of 10 patients who would have been eligible for this study, and the techniques were compared in terms of doses to the target volumes and the organs at risk. The IMRT method resulted in much greater sparing of the rectum and bladder than the 3DCRT technique, whilst still delivering acceptable doses to the target volumes. In particular, the volume of rectum receiving the minimum PTV dose of 47.5 Gy was reduced from a mean value of 36.9% (range 23.4% to 61.0%) to 18.6% (10.3% to 29.0%). In conclusion, it was found possible to use a class solution approach to produce IMRT dose escalated plans. This IMRT technique has since been implemented clinically for patients enrolled in the hypofractionated dose escalation study.     

Intensity-modulated radiotherapy for a prostate patient with a metal prosthesis

When treating prostate patients having a metallic prosthesis with radiation, a 3D conformal radiotherapy (3DCRT) treatment plan is commonly created using only those fields that avoid the prosthesis in the beam’s-eye view (BEV). With a limited number of portals, the resulting plan may compromise the dose sparing of the rectum and bladder. In this work, we investigate the feasibility of using intensity-modulated radiotherapy (IMRT) to treat prostate patients having a metallic prosthesis. Three patients, each with a single metallic prosthesis, who were previously treated at the University of Chicago Medical Center for prostate cancer, were selected for this study. Clinical target volumes (CTV = prostate + seminal vesicles), bladder, and rectum volumes were identified on CT slices. Planning target volumes (PTV) were generated in 3D by a 1-cm expansion of the CTVs. For these comparative studies, treatment plans were generated from CT data using 3DCRT and IMRT treatment planning systems. The IMRT plans used 9 equally-spaced 6-MV coplanar fields, with each field avoiding the prosthesis. The 3DCRT plans used 5 coplanar 18-MV fields, with each field avoiding the prosthesis. A 1-cm margin around the PTV was used for the blocks. Each of the 9-field IMRT plans spared the bladder and rectum better than the corresponding 3DCRT plan. In the IMRT, plans, a bladder volume receiving 80% or greater dose decreased by 20–77 cc, and a volume rectal volume receiving 80% or greater dose decreased by 24–40 cc. One negative feature of the IMRT plans was the homogeneity across the target, which ranged from 95% to 115%.     

Evaluation of incidental testicular dose with thermoluminescence dosimetry during prostate radiotherapy

The aim of this study was to investigate incidental testicular doses during intensity modulated radiation therapy (IMRT) in patients treated with prostate radiotherapy only (PORT) and whole pelvis radiotherapy (WPRT). A total of 34 prostate cancer patients with intermediate and high risk were included in this prospective study. Each patient in the intermediate risk group received a total of 78 Gy in 39 fractions for prostate and seminal vesicles. In patients in the high risk group, 2 Gy daily fraction dose for pelvic lymphatics was given to 50 Gy, and then 78 Gy was given to prostate and seminal vesicles volumes. Treatment plans were created for all patients using the IMRT technique with 6MV. Testicular doses were measured for WPRT and PORT by thermoluminescence dosimetry (TLD) detectors placed on testis surface. Testicular doses measured for WPRT and PORT were compared. The isocenter to testicular distance for WPRT and PORT was 16.83-cm (13.20 to 18.80-cm) and 11.15 cm (9.10 to 13.00-cm), respectively. The mean testicular dose measurements of TPS and TLD per fraction during PORT were 2.41 cGy (1.95 to 3.60 cGy) and 3.70 cGy (2.80 to 5.10 cGy), respectively (p = 0.00). In WPRT irradiation, mean testicular dose values of TPS and TLD per fraction were measured as 3.85 cGy (2.00 to 5.70 cGy) and 5.85 cGy (4.25 to 7.55 cGy), respectively (p = 0.00). The cumulative mean scattered dose for PORT irradiation of 78 Gy in 39 fractions was 144.30 cGy. The mean cumulative dose received by the testis for the high-risk prostate patient was 228.15 cGy. There was a significant difference in testicular dose between WPRT and PORT irradiation. Testicular doses decreased significantly with increasing isocenter-testis distance. Incidental testicular dose during prostate radiotherapy can be significantly detrimental to spermatogenesis. Therefore, the testicles should be contoured as an organ at risk for the estimation of absorbed doses. The use of in vivo dosimetry is recommended for accurate measurement of testicular dose in radiotherapy of prostate cancer for men desiring continued fertility.     

Influence of high-definition multileaf collimator for three-dimensional conformal radiotherapy and intensity-modulated radiotherapy of prostate cancer

The focus of this work is to evaluate the dosimetric impact of treatment planning for three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) of prostate cancer using Varian/BrainLAB 120-leaf high-definition multileaf collimator (HD120 MLC) with 2.5 mm leaf width and Varian 120-leaf millennium multileaf collimator (M120 MLC) with 5 mm leaf width. We measured the leaf transmission and dosimetric leaf gap (DLG) of two multileaf collimator (MLC) systems using Farmer ionization chamber. The dosimetric impact of treatment planning for 3DCRT and IMRT of prostate cancer for ten clinical cases using two MLC systems was evaluated quantitatively. 3DCRT was divided to 3DCRT(middle) as fitting at middle of leaf tip and 3DCRT(outside) as fitting at outside of leaf tip. The leaf transmission factor and DLG of HD120 MLC for 6 and 10 MV X-ray decreased by 0.2% and 1 mm, respectively, compared to M120 MLC. The mean conformity index of PTV of treatment planning for prostate 3DCRT(middle), 3DCRT(outside) , and IMRT decreased by 0.9%, 6.6%, and 0.9% and the mean homogeneity index increased 2.3%, 13.0%, and 4.2%, respectively. The mean V20, V40, and V65 decreased by 2.4%, 6.6%, and 4.5% for bladder and 3.3%, 6.1%, and 5.9% for rectum, respectively. The results of this work demonstrated that the dose conformity of PTV improved and the dose of bladder and rectum decreased for 3DCRT and IMRT of prostate cancer using HD120 MLC compared to M120 MLC, because of reduction of leaf width, leaf transmission, and rounded leaf end transmission.     

Dosimetric advantage and clinical implication of a micro-multileaf collimator in the treatment of prostate with intensity-modulated radiotherapy.

This paper investigates the dosimetric benefits of a micro-multileaf (4-mm leaf width) collimator (mMLC) for intensity-modulated radiation therapy (IMRT) treatment planning of the prostate cancer and its potential application for dose escalation and hypofractionation. We compared treatment plans for IMRT delivery using 2 different multileaf collimator (MLC) leaf widths (4 vs. 10 mm) for 10 patients with prostate cancer. Treatment planning was performed on the XknifeRT2 treatment planning system. All beams and optimization parameters were identical for the mMLC and MLC plans. All of the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose (74 Gy). The differences in dose distribution between the 2 groups of plans using the mMLC and the MLC were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. Significant reductions in the volume of rectum receiving medium to higher doses were achieved using the mMLC. The average decrease in the volume of the rectum receiving 40, 50, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p-values less than 0.0001 for V40 and V50 and 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum were 20.0% (p < 0.0001) and 18.3% (p < 0.0002), respectively, when compared to those with the MLC plans. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 32%. In the high-dose range, there was no significant difference in the dose deposited in the "hottest" 1 cc of the rectum between the 2 MLC plans for all cases (p > 0.78). Because of the reduction of rectal volume receiving medium to higher doses, dose to the prostate target can be escalated by about 20 Gy to over 74 Gy, while keeping the rectal dose (either denoted by D17 or D35) the same as those with the use of the MLC. The maximum achievable dose, derived when the rectum is allowed to reach the tolerance level, was found to be in the range of 113-172 Gy (using the tolerance value of D17). We conclude that the use of the mMLC for IMRT of the prostate may facilitate dose hypofractionation due to its dosimetric advantage in significantly improving the DVH parameters of the prostate and critical organs. When used for conventional fractionation scheme, mMLC for IMRT of the prostate may reduce the toxicity to the critical organs.     

A case study of radiotherapy planning for a bilateral metal hip prosthesis prostate cancer patient.

The purpose of this report is to communicate the observed advantage of intensity-modulated radiotherapy (IMRT) in a patient with bilateral metallic hip prostheses. In this patient with early-stage low-risk disease, a dose of 74 Gy was planned in two phases--an initial 50 Gy to the prostate and seminal vesicles and an additional 24 Gy to the prostate alone. Each coplanar beam avoided the prosthesis in the beam's eye view. Using the same target expansions for each phase, IMRT and 3D-conformal radiotherapy (CRT) plans were compared for target coverage and inhomogeneity as well as dose to the bladder and rectum. The results of the analysis demonstrated that IMRT provided superior target coverage with reduced dose to normal tissues for both individual phases of the treatment plan as well as for the composite treatment plan. The dose to the rectum was significantly reduced with the IMRT technique, with a composite V 80 of 35% for the IMRT plan versus 70% for 3D-CRT plan. Similarly, the dose to the bladder was significantly reduced with a V 80 of 9% versus 20%. Overall, various dosimetric parameters revealed the corresponding 3D-CRT plan would not have been acceptable. The results indicate significant success with IMRT in a clinical scenario where there were no curative alternatives for local treatment other than external beam radiotherapy. Therefore, definitive external beam radiation of prostate cancer patients with bilateral prosthesis is made feasible with IMRT. The work described herein may also have applicability to other groups of patients, such as those with gynecological or other pelvic malignancies.     

IMRT to Escalate the Dose to the Prostate while Treating the Pelvic Nodes

Background and Purpose: To assess and quantify the benefit of introducing intensity–modulated radiotherapy (IMRT) over conventional approaches to cover the pelvic nodes while escalating the dose to the prostate gland.Material and Methods: The pelvic lymphatics were planned to receive 50 Gy at 2 Gy per fraction by four–field box (4FB) technique and standard field blocks drawn on digitally reconstructed radiographs (DRR), 4FB with field blocks according to the position of pelvic nodes as contoured on serial planning CT slices, or IMRT. The lateral fields included three different variations of field blocks to assess the role of various degrees of rectal shielding. The boost consisted in 26 Gy in 13 fractions delivered via six–field three–dimensional conformal radiotherapy (3DCRT) or IMRT. By the combination of a pelvic treatment and boost, several plans were obtained for each patient, all normalized to be isoeffective with regard to prostate–planning target volume (PTV–P) coverage. Plans were compared with respect to dose–volume histogram (DVH) of pelvic nodes/seminal vesicles–PTV (PTV–PN/SV), rectum, bladder and intestinal cavity. Reported are the results obtained in eight patients.Results: Pelvic IMRT with a conformal boost provided superior sparing of both bladder and rectum over any of the 4FB plans with the same boost. For the rectum the advantage was around 10% at V70 and even larger for lower doses. Coverage of the pelvic nodes was adequate with initial IMRT with about 98% of the volume receiving 100% of the prescribed dose. An IMRT boost provided a gain in rectal sparing as compared to a conformal boost. However, the benefit was always greater with pelvic IMRT followed by a conformal boost as compared to 4FB with IMRT boost. Finally, the effect of utilizing an IMRT boost with initial pelvic IMRT was greater for the bladder than for the rectum (at V70, about 9% and 3% for the bladder and rectum, respectively).Conclusion: IMRT to pelvic nodes with a conformal boost allows dose escalation to the prostate while respecting current dose objectives in the majority of patients and it is dosimetrically superior to 4FB. An IMRT boost should be considered for patients who fail to meet bladder dose objectives.     

Comparison of IMRT and VMAT plans with different energy levels using Monte-Carlo algorithm for prostate cancer

Purpose

To make dosimetric comparisons of volumetric-modulated arc therapy (VMAT) and 7-field intensity-modulated radiotherapy (IMRT) with dynamic MLCs using the Monaco treatment planning system with Monte Carlo algorithm.

Materials and methods

Single-arc VMAT and 7-field IMRT treatment plans were compared for 12 intermediate risk prostate cancer patients treated with prostate and seminal vesicle radiotherapy. For all patients, the prescribed dose was 78 Gy delivered in 39 fractions. The dosimetric data of IMRT and VMAT plans with 6, 10 and 15 MV energies were compared. The comparison was made for target volume, organs at risk (OAR) doses, and for monitor units (MU).

Results

The normal tissue surrounding the target were lower in VMAT plans compared to IMRT plans. VMAT plans achieved lower doses to all OARs for nearly all dosimetric endpoints. VMAT plans achieved 9.4, 9.0 and 7.0 % relative decrease in MUs required for RT delivery, for 6, 10 and 15 MV energy levels, respectively. The target volume and OAR dosimetric values did not differ significantly between 6, 10 and 15 MV photon energies.

Conclusion

VMAT plans were found to be dosimetrically equivalent to IMRT plans for prostate cancer patients, with better rectum and bladder sparing and fewer MUs required.     

Toxicity and outcome of pelvic IMRT for node-positive prostate cancer

Background and purpose

This study reports on the treatment techniques, toxicity, and outcome of pelvic intensity-modulated radiotherapy (IMRT) for lymph node-positive prostate cancer (LNPPC, T1-4, c/pN1 cM0).

Patients and methods

Pelvic IMRT to 45–50.4?Gy was applied in 39?cases either after previous surgery of involved lymph nodes (n?=?18) or with a radiation boost to suspicious nodes (n?=?21) with doses of 60–70?Gy, usually combined with androgen deprivation (n?=?37). The prostate and seminal vesicles received 70–74?Gy. In cases of previous prostatectomy, prostatic fossa and remnants of seminal vesicles were given 66–70?Gy. Treatment-related acute and late toxicity was graded according to the RTOG criteria.

Results

Acute radiation-related toxicity higher than ?grade?2 occurred in 2?patients (with the need for urinary catheter/subileus related to adhesions after surgery). Late toxicity was mild (grade 1–2) after a median follow-up of 70?months. Over 50% of the patients reported no late morbidity (grade 0). PSA control and cancer-specific survival reached 67% and 97% at over ?5?years.

Conclusion

Pelvic IMRT after the removal of affected nodes or with a radiation boost to clinically positive nodes led to an acceptable late toxicity (no grade 3/4 events), thus justifying further evaluation of this approach in a larger cohort.     

Direct Segment Aperture and Weight Optimization for Intensity-Modulated Radiotherapy of Prostate Cancer

BACKGROUND AND PURPOSE: To describe the implementation and to evaluate the results of direct segment aperture optimization using the segment outline and weight adapting tool (SOWAT) in intensity-modulated radiotherapy (IMRT) for prostate cancer. PATIENTS AND METHODS: 14 consecutive, unselected patients with localized prostate cancer were entered in a planning study comparing IMRT without and with the use of SOWAT. The clinical target volume (CTV) consisted of the prostate and seminal vesicles in all cases. To create the planning target volume (PTV), a three-dimensional anisotropic margin (10 mm in craniocaudal direction, 7 mm in both other directions) was used. To compare both plans, physical as well as biological endpoints were considered. RESULTS: Considering the CTV, SOWAT resulted in a significantly higher minimal dose together with a higher dose to 95% (D(95)) and 90% (D(90)) of the CTV volume (p < 0.05; Figure 2). Target dose homogeneity was significantly improved (p < 0.001). Tumor control probability (TCP) was significantly increased (p < 0.05). Considering the PTV, D(90) was significantly increased (p < 0.05). Target dose homogeneity was significantly improved (p < 0.05; Figure 1). For rectum, the volumes receiving 50 Gy (R(vol50)), 60 Gy (R(vol60)), or 65 Gy (R(vol65)) as well as the mean dose were significantly lowered after SOWAT (p = 0.0001; Figure 3). Rectal normal tissue complication probability (NTCP) was significantly lower after SOWAT (p = 0.005). Probability of uncomplicated local control (P+) was significantly higher after SOWAT (p < 0.0001). CONCLUSION: SOWAT is a powerful planning tool to increase the therapeutic ratio of IMRT for prostate cancer. It leaves the delivery time unchanged, so that treatments can still be delivered within a time slot of 8 min.     

RapidArc radiotherapy planning for prostate cancer: Single-arc and double-arc techniques vs. intensity-modulated radiotherapy

RapidArc is a novel technique using arc radiotherapy aiming to achieve intensity-modulated radiotherapy (IMRT)-quality radiotherapy plans with shorter treatment time. This study compared the dosimetric quality and treatment efficiency of single-arc (SA) vs. double-arc (DA) and IMRT in the treatment of prostate cancer. Fourteen patients were included in the analysis. The planning target volume (PTV), which contained the prostate gland and proximal seminal vesicles, received 76 Gy in 38 fractions. Seven-field IMRT, SA, and DA plans were generated for each patient. Dosimetric quality in terms of the minimum PTV dose, PTV hotspot, inhomogeneity, and conformity index; and sparing of rectum, bladder, and femoral heads as measured by V70, V-40, and V20 (% of volume receiving >70 Gy, 40 Gy, and 20 Gy, respectively), treatment efficiency as assessed by monitor units (MU) and treatment time were compared. All plan objectives were met satisfactorily by all techniques. DA achieved the best dosimetric quality with the highest minimum PTV dose, lowest hotspot, and the best homogeneity and conformity. It was also more efficient than IMRT. SA achieved the highest treatment efficiency with the lowest MU and shortest treatment time. The mean treatment time for a 2-Gy fraction was 4.80 min, 2.78 min, and 1.30 min for IMRT, DA, and SA, respectively. However, SA also resulted in the highest rectal dose. DA could improve target volume coverage and reduce treatment time and MU while maintaining equivalent normal tissue sparing when compared with IMRT. SA achieved the greatest treatment efficiency but with the highest rectal dose, which was nonetheless within tolerable limits. For busy units with high patient throughput, SA could be an acceptable option.     

Reducing the Risk of Xerostomia and Mandibular Osteoradionecrosis: The Potential Benefits of Intensity Modulated Radiotherapy in Advanced Oral Cavity Carcinoma

Radiation therapy for squamous cell carcinoma of the oral cavity may be curative, but carries a risk of permanent damage to bone, salivary glands, and other soft tissues. We studied the potential of intensity modulated radiotherapy (IMRT) to improve target volume coverage, and normal tissue sparing for advanced oral cavity carcinoma (OCC). Six patients with advanced OCC requiring bilateral irradiation to the oral cavity and neck were studied. Standard 3D conformal radiotherapy (3DCRT) and inverse-planned IMRT dose distributions were compared by using dose-volume histograms. Doses to organs at risk, including spinal cord, parotid glands, and mandible, were assessed as surrogates of radiation toxicity. PTV1 mean dose was 60.8 ± 0.8 Gy for 3DCRT and 59.8 ± 0.1 Gy for IMRT (p = 0.04). PTV1 dose range was 24.7 ± 6 Gy for 3DCRT and 15.3 ± 4 Gy for IMRT (p = 0.001). PTV2 mean dose was 54.5 ± 0.8 Gy for 3DCRT and for IMRT was 54.2 ± 0.2 Gy (p = 0.34). PTV2 dose range was improved by IMRT (7.8 ± 3.2 Gy vs. 30.7 ± 12.8 Gy, p = 0.006). Homogeneity index (HI) values for PTV2 were closer to unity using IMRT (p = 0.0003). Mean parotid doses were 25.6 ± 2.7 Gy for IMRT and 42.0 ± 8.8 Gy with 3DCRT (p = 0.002). The parotid V30 in all IMRT plans was <45%. The mandible V50, V55, and V60 were significantly lower for the IMRT plans. Maximum spinal cord and brain stem doses were similar for the 2 techniques. IMRT provided superior target volume dose homogeneity and sparing of organs at risk. The magnitude of reductions in dose to the salivary glands and mandible are likely to translate into reduced incidence of xerostomia and osteoradionecrosis for patients with OCC.     

VMAT partial arc technique decreases dose to organs at risk in whole pelvic radiotherapy for prostate cancer when compared to full arc VMAT and IMRT

Whole pelvic radiotherapy (WPRT) can sterilize microscopic lymph node metastases in treatment of prostate cancer. WPRT, compared to prostate only radiotherapy (PORT), is associated with increased acute gastrointestinal, and hematological toxicities. To further explore minimizing normal tissue toxicities associated with WPRT in definitive IMRT for prostate cancer, this planning study compared dosimetric differences between static 9-field-IMRT, full arc VMAT, and mixed partial-full arc VMAT techniques. In this retrospective study, 12 prostate cancer patients who met the criteria for WPRT were randomly selected for this study. The initial volume, PTV46, included the prostate, seminal vesicles, and pelvic nodes with margin and was prescribed to 4600 cGy. The cone-down volume, PTV78, included the prostate and proximal seminal vesicles with margin to a total dose of 7800 cGy. For each CT image set, 3 plans were generated for each of the PTVs: an IMRT plan, a full arc (FA) VMAT plan, and a mixed partial-full arc (PFA) VMAT plan, using 6MV photons energy. According to RTOG protocols none of the plans had a major Conformity Index (CI) violation by any of the 3 planning techniques. PFA plan had the best mean CI index of 1.00 and significantly better than IMRT (p = 0.03) and FA (p = 0.007). For equivalent PTV coverage, the average composite gradient index of the PFA plans was better than the IMRT and the FA plans with values 1.92, 2.03, and 2.01 respectively. The defference was statistically significant between PFA/IMRT and PFA/FA, with p- values of < 0.001. The IMRT plans and the PFA plans provided very similar doses to the rectum, bladder, sigmoid colon, and femoral heads, which were lower than the dose in the FA plans. There was a significant decrease in the mean dose to the rectum from 4524 cGy with the FA to 4182 cGy with the PFA and 4091 cGy with IMRT (p < 0.001). The percent of rectum receiving 4000 cGy was also the highest with FA at 66.1% compared to 49.9% (PFA) and 47.5% (IMRT). There was a significant decrease in the mean dose to the bladder from 3922 cGy (FA) to 3551 cGy (PFA) and 3612 cGy (IMRT) (p < 0.001). The percent of bladder receiving 4000 cGy was also the highest with FA at 45.4% compared to 36.6% (PFA) and 37.4% (IMRT). The average mean dose to the sigmoid colon decreased from 4177 cGy (FA) to 3893 cGy (PFA) and 3819 cGy (IMRT). The average mean dose to the femoral heads decreased from 2091 cGy (FA) to 2026 cGy (PFA) and 1987 cGy (IMRT). Considering the improvement in plan quality indices recorded in this study including the dose gradient and the dose to organs at risk, mixed partial-full arc plans may be the preferred VMAT treatment technique over full arc plans for prostate cancer treatments that include nodal volumes.     

Feasibility of IMRT to Cover Pelvic Nodes While Escalating the Dose to the Prostate Gland: Dosimetric Data on 35 Consecutive Patients

Utilizing available dosimetric and acute toxicity data, we confirm the feasibility of intensity modulated radiotherapy (IMRT) to include treatment of the pelvic nodes (PN) while escalating the dose to the prostate. Data were obtained from 35 consecutive patients with prostate cancer with ≥15% risk of PN involvement. Patients received an initial boost to the prostate, delivering 16 Gy over 8 fractions using a 6-field conformal technique, followed by an 8-field coplanar inverse planning IMRT technique delivering an additional 60 Gy over 30 fractions to the prostate (76 Gy total) and 54 Gy over 30 fractions to the seminal vesicles (SV) and PN. Dose-volume histogram analysis was performed for planning target volumes and organs at risk. Acute toxicity (RTOG/EORTC scale) was prospectively and independently scored weekly for each patient. The maximum, mean, minimum dose, and D95 to each planning target volume is provided: prostate (82.2, 78.2, 72.6, 75.2 Gy), SV (79.0, 72.5, 56.9, 61.1 Gy), and PN (80.4, 59.7, 46.5, 53.3 Gy), respectively. The percent volume receiving a dose at or above “x” Gy (Vx) was recorded for V75, V70, V65, V60, and V50 as: bladder (14%, 24%, 32%, 39%, and 54%) and rectum (3%, 18%, 26%, 34%, and 51%), respectively. Acute toxicity was as follows: 54% grade 2+ GI (n = 19), 25% grade 2+ GU (n = 9). IMRT enables treatment of pelvic nodes while escalating dose to the prostate and is clinically feasible with acute toxicity within expected ranges.