A treatment planning study comparing helical tomotherapy with intensity-modulated radiotherapy for the treatment of anal cancer

Purpose

A planning study to compare helical tomotherapy (HT) and intensity-modulated radiotherapy (IMRT) for the treatment of anal canal cancer.

Materials and methods

Sixteen (8 males and 8 females) patients with anal cancer previously treated radically were identified. HT and IMRT plans were generated and dosimetric comparisons of the plans were performed. The planning goals were to deliver 54 Gy to the tumor (PTV_54Gy) and 48 Gy to the nodes at risk (PTV_Node) in 30 fractions.

Results

PTVs: HT plans were more homogeneous for both men and women. Male patients: HT vs. IMRT: D_max: 55.87 ± 0.58 vs. 59.17 ± 3.24 (p = 0.036); D_min: 52.91 ± 0.36 vs. 44.09 ± 6.84 (p = 0.012); female patients: HT vs. IMRT: D_max: 56.14 ± 0.71 vs. 59.47 ± 0.81 (p = 0.012); D_min: 52.36 ± 0.87 vs. 50.97 ± 1.42 (p = 0.028). OARs: In general, HT plans delivered a lower dose to the peritoneal cavity, external genitalia and the bladder and IMRT plans resulted in greater sparing of the pelvic bones (iliac crest/femur) for both men and women. Iliac crest/femur: the difference was significant only for the mean V10 Gy of iliac crest in women (p ? 0.012). External genitalia: HT plans achieved better sparing in women compared to men (p ? 0.046). For men, the mean doses were 18.96 ± 3.17 and 15.72 ± 3.21 for the HT and IMRT plan, respectively (p ? 0.017). Skin: both techniques achieved comparable sparing of the non-target skin (p = NS).

Conclusions

HT and IMRT techniques achieved comparable target dose coverage and organ sparing, whereas HT plans were more homogeneous for both men and women.     

Volumetric modulated arc therapy versus conventional intensity modulated radiation therapy for stereotactic spine radiotherapy: A planning study and early clinical data

Background and purpose

Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiation therapy (SBRT). As target geometry is complex, we compared SBRT plans using volumetric modulated arc radiotherapy (RapidArc®, RA) and conventional intensity-modulated radiotherapy (IMRT).

Materials and methods

RA and IMRT plans to deliver a fraction of 16 Gy to at least 90% of planning target volume (PTV) were compared for PTV coverage, normal organ sparing and estimated delivery times. Group 1 consisted of PTVs to only vertebral body (n = 3), while group 2 had PTVs encompassing the entire vertebra (n = 4). Finally, RA delivery parameters in four patients were assessed.

Results

Both techniques delivered 16 Gy to a mean of 95% and 85% of the PTV in groups 1 and 2, respectively. Spinal cord sparing was comparable; mean V_{10-partial cord} for RA and IMRT in group 1 was 3.6%, and was 9.4% versus 11.5%, respectively, in group 2. Estimated mean treatment times for RA with 2-3 arcs and IMRT were comparable. Clinical RA beam-on times ranged from 11 to 15.4 min.

Conclusions

Both RA and conventional IMRT plans deliver high quality vertebral SBRT, but plan quality was poorer when the PTV consisted of the entire vertebra.     

Electron arc therapy for bilateral chest wall irradiation: treatment planning and dosimetric study

Aims

The treatment of patients with synchronous bilateral breast cancer is a challenge. We present a report of dosimetric data of patients with bilateral chest walls as the target treated with electron arc therapy.

Materials and methods

Ten consecutive patients who had undergone electron arc therapy to the bilateral chest wall for breast cancer were analysed. After positioning and immobilisation, patients underwent computed tomography scans from the neck to the upper abdomen. Electron arc plans were generated using the PLATO RTS (V1.8.2 Nucletron) treatment planning system. Electron energy was chosen depending upon the depth and thickness of the planning target volume (PTV). For all patients, the arc angle ranged between 80 and 280° (start angle 80°, stop angle 280°). The homogeneity index, coverage index and doses to organs at risk were evaluated. The patient-specific output factor and thermoluminescence dosimetry (TLD) measurements were carried out for all patients. The total planned dose to the PTV was 50 Gy/25 fractions/5 weeks.

Results

The mean PTV (± standard deviation) was 568.9 (±116) cm³. The mean PTV coverage was 89 (±5.8)% of the prescribed dose. For the right lung, the mean values of D₁ and D₁₀ were 46 (±7.6) and 30 (±9) Gy, respectively. For the left lung, the mean values of D₁ and D₁₀ were 45 (±7) and 27 (±8) Gy, respectively. For the heart, the mean values of D₁, D₅ and D₁₀ were 21 (±15), 13.5 (±12) and 9 (±9) Gy, respectively. The mean values of TLD at various pre-specified locations on the chest wall surface were 1.84, 1.82, 1.82, 1.89 and 1.78 Gy, respectively

Conclusion

The electron arc technique for treating the bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, compared with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery.     

Correlation of dose-volume parameters, endoscopic and clinical rectal side effects in cervix cancer patients treated with definitive radiotherapy including MRI-based brachytherapy

Purpose

Correlation of dosimetric parameters for MRI-based 3D treatment planning with rectoscopic findings and clinical rectal side effects.

Methods and materials

Rectosigmoidoscopy and rectal morbidity assessment were performed on 35 cervical cancer patients treated with external beam radiotherapy (EBRT) and HDR-intracavitary brachytherapy (ICB). The total doses, normalised to 2 Gy fractions (EQD2, α/β = 3 Gy), in 0.1, 1.0 and 2.0 cm³ (D_0.1cc, D_1cc, D_2cc) of rectum were determined by summation of EBRT and ICB plans. Correlation analysis between clinical symptoms (LENT/SOMA) and rectoscopic changes (Vienna Rectoscopy Score, VRS) was performed. For dose-response analyses, the logit model was applied.

Results

Mean follow-up was 18 months. LENT/SOMA score was 1 in 4 patients, 2 in 8 patients, 4 in 1 patient. Telangiectasia was found in 26 patients (74%), five of them had ulceration corresponding to the 0.1 cm³ volume (anterior wall). Mean values D_0.1cc, D_1cc, and D_2cc were 81 ± 13, 70 ± 9 and 66 ± 8 Gy, respectively. The ED50 values for VRS ? 3 and for LENT/SOMA ? 2 significantly increased with decreasing volumes. D_2cc was higher in patients with VRS ? 3 compared to VRS < 3 (72 ± 6 vs 62 ± 7 Gy; p < 0.001) and in symptomatic vs asymptomatic patients (72 ± 6 vs 63±8 Gy; p < 0.001). VRS correlated with the LENT/SOMA score.

Conclusions

Rectosigmoidoscopy is sensitive in detecting mucosal changes, independent of clinical symptoms. The localization of these changes corresponds to the high dose volumes as defined by imaging. The development of mucosal and clinical changes in the rectum follows a clear dose-effect and volume-effect. DVH parameters could be established.     

A study of middle ear function in the treatment of nasopharyngeal carcinoma with IMRT technique

Purpose

This study evaluates the difference in damage to middle ear function with CRT and IMRT techniques in the treatment of nasopharyngeal carcinoma (NPC). We explore the isthmus of the Eustachian tube (ET) as the key anatomic site for the prevention of radiation-induced otitis media with effusion.

Methods and materials

Eighty-two patients with NPC were divided into two groups: 40 patients treated with CRT and 42 patients treated with IMRT. The difference between dosage over the middle ear cavity and the isthmus of the ET was evaluated in both CRT group and IMRT group. All patients underwent hearing tests including pure tone audiometry and impedance audiometry before and after RT.

Results

The dosage difference to the middle ear cavity and isthmus between these two groups was statistically significant (p < 0.05). The difference in hearing test results between these two groups was also statistically significant (p < 0.05). If we limited the dose to the middle ear cavity under 34 Gy and the dose to the isthmus under 53 Gy with IMRT, we may decrease radiation-induced OME even with the larger 2.25 Gy fraction size.

Conclusions

IMRT may have better protected the middle ear function compared with the CRT technique, even with larger fraction sizes than for the conventional CRT technique.     

Decline of dose coverage between intraoperative planning and post implant dosimetry for I-125 permanent prostate brachytherapy: Comparison between loose and stranded seed implants

Background and purpose

In permanent prostate brachytherapy the dose distributions 4 weeks post implant differ from the intraoperative dose distributions. The purpose of this study is to compare intraoperative planning and post implant dosimetry for loose and stranded seed implants.

Materials and methods

This study investigates prostate dose coverage in 389 patients with stage T1 or T2 prostate cancer treated in the years 2005, 2006 and 2007. The patients received either a loose seed or a stranded seed implant. All patients had US-based intraoperative planning and CT/MRI-based post implant dosimetry after 4 weeks.

Results

Intraoperative and post implant D₉₀ values amounted 183 ± 13 Gy (mean ± standard deviation) and 161 ± 30 Gy, respectively. Decline of D₉₀ values (mean and 95% confidence interval) between intraoperative planning and post implant dosimetry for RAPID strand (n = 67), Intersource strand (n = 136) and loose selectSeeds (n = 186) implants amounted to −40 (−45 to −34) Gy, −25 (−28 to −21) Gy and −15 (−18 to −21) Gy, respectively.

Conclusions

The patients treated in the period 2005-2007 with stranded or loose seed implants had on average adequate D₉₀ values of 161 ± 30 Gy. Post implant D₉₀ values were 22 ± 27 Gy lower compared to intraoperative planning. Decline of dose coverage between intraoperative planning and post implant dosimetry was significantly larger for the stranded seed implants.     

Integrated-boost IMRT or 3-D-CRT using FET-PET based auto-contoured target volume delineation for glioblastoma multiforme - a dosimetric comparison

Purpose

A study was performed comparing dosimetric characteristics of volumetric modulated arcs (RapidArc, RA) and fixed field intensity modulated therapy (IMRT) on patients with bilateral breast carcinoma.

Materials and methods

Plans for IMRT and RA, were optimised for 10 patients prescribing 50 Gy to the breast (PTVII, 2.0 Gy/fraction) and 60 Gy to the tumour bed (PTVI, 2.4 Gy/fraction). Objectives were: for PTVs V_90%>95%, D_max<107%; Mean lung dose MLD<15 Gy, V_{20 Gy}<22%; heart involvement was to be minimised. The MU and delivery time measured treatment efficiency. Pre-treatment dosimetry was performed using EPID and a 2D-array based methods.

Results

For PTVII minus PTVI, V_90% was 97.8 ± 3.4% for RA and 94.0 ± 3.5% for IMRT (findings are reported as mean ± 1 standard deviation); D_5%-D_95% (homogeneity) was 7.3 ± 1.4 Gy (RA) and 11.0 ± 1.1 Gy (IMRT). Conformity index (V_95%/V_PTVII) was 1.10 ± 0.06 (RA) and 1.14 ± 0.09 (IMRT). MLD was <9.5 Gy for all cases on each lung, V_{20 Gy} was 9.7 ± 1.3% (RA) and 12.8 ± 2.5% (IMRT) on left lung, similar for right lung. Mean dose to heart was 6.0 ± 2.7 Gy (RA) and 7.4 ± 2.5 Gy (IMRT). MU resulted in 796 ± 121 (RA) and 1398 ± 301 (IMRT); the average measured treatment time was 3.0 ± 0.1 minutes (RA) and 11.5 ± 2.0 (IMRT). From pre-treatment dosimetry, % of field area with γ <1 resulted 98.8 ± 1.3% and 99.1 ± 1.5% for RA and IMRT respectively with EPID and 99.1 ± 1.8% and 99.5 ± 1.3% with 2D-array (ΔD = 3% and DTA = 3 mm).

Conclusion

RapidArc showed dosimetric improvements with respect to IMRT, delivery parameters confirmed its logistical advantages, pre-treatment dosimetry proved its reliability.     

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

Introduction

Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques.

Methods

Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200° rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D_95% (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered.

Results

For MIMiC/IMRT_MLC/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving ?70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for ? 50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for ? 30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D_95% was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min.

Conclusion

All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.     

Does atlas-based autosegmentation of neck levels require subsequent manual contour editing to avoid risk of severe target underdosage? A dosimetric analysis

Background and purpose

To investigate the dosimetric impact of not editing auto-contours of the elective neck and organs at risk (OAR), generated with atlas-based autosegmentation (ABAS) (Elekta software) for head and neck cancer patients.

Materials and methods

For nine patients ABAS auto-contours and auto-contours edited by two observers were available. Based on the non-edited auto-contours clinically acceptable IMRT plans were constructed (designated ‘ABAS plans’). These plans were then evaluated for the two edited structure sets, by quantifying the percentage of the neck-PTV receiving more than 95% of the prescribed dose (V₉₅) and the near-minimum dose (D₉₉) in the neck PTV. Dice coefficients and mean contour distances were calculated to quantify the similarity of ABAS auto-contours with the structure sets edited by observer 1 and observer 2. To study the dosimetric importance of editing OAR auto-contours a new IMRT plan was generated for each patient-observer combination, based on the observer’s edited CTV and the non-edited salivary gland auto-contours. For each plan mean doses for the non-edited glands were compared with doses for the same glands edited by the observer.

Results

For both observers, edited neck CTVs were larger than ABAS auto-contours (p ? 0.04), by a mean of 8.7%. When evaluating ABAS plans on the PTVs of the edited structure sets, V₉₅ reduced by 7.2% ± 5.4% (1 SD) (p < 0.03). The mean reduction in D₉₉ was 14.2 Gy (range 1-54 Gy). Even for Dice coefficients >0.8 and mean contour distances <1 mm, reductions in D₉₉ up to 11 Gy were observed. For treatment plans based on observer PTVs and non-edited auto-contoured salivary glands, the mean doses in the edited glands differed by only −0.6 Gy ± 1.0 Gy (p = 0.06).

Conclusions

Editing of auto-contoured neck CTVs generated by ABAS is required to avoid large underdosages in target volumes. Often used similarity measures for evaluation of auto-contouring algorithms, such as dice coefficients, do not predict well for expected PTV underdose. Editing of salivary glands is less important as mean doses achieved for non-edited glands predict well for edited structures.     

Dose-response relationship for radiation-induced pneumonitis after pulmonary stereotactic body radiotherapy

Purpose

To evaluate dosimetric factors predictive for radiation-induced pneumonitis (RP) after pulmonary stereotactic body radiotherapy (SBRT).

Materials and methods

A retrospective analysis was performed based on 59 consecutive patients treated with cone-beam CT-based image-guided SBRT for primary NSCLC (n = 21) or pulmonary metastases (n = 54). The majority of patients were treated with radiosurgery of 26 Gy to 80% (n = 29) or three fractions of 12.5 Gy to 65% (n = 40). To correct for different single fraction doses, local doses were converted to 2 Gy equivalent normalized total doses (NTDs) using α/β ratio of 3 Gy for RP. Dose-volume parameters and incidences of RP ? grade II SWOG were fitted using NTCP models.

Results

Eleven patients developed RP grade II. With an average MLD of 10.3 ± 5.6 Gy to the ipsilateral lung, a significant dose-response relationship was observed: the MLD was 12.5 ± 4.3 Gy and 9.9 ± 5.8 Gy for patients with and without development of RP, respectively. Additionally, volumes of the lung exposed to minimum doses between 2.5 and 50 Gy (V_2.5-V₅₀) were correlated with incidences of RP with a continuous decrease of the goodness of fit for higher doses.

Conclusions

The MLD and V_2.5-V₅₀ of the ipsilateral lung were correlated with incidences of RP after pulmonary SBRT.     

Endorectal balloons in the post prostatectomy setting: Do gains in stability lead to more predictable dosimetry?

Purpose

To perform a comparative study assessing potential benefits of endorectal-balloons (ERB) in post-prostatectomy patients.

Method and materials

Ten retrospective post-prostatectomy patients treated without ERB and ten prospective patients treated with the ERB in situ were recruited. All patients received IMRT and IGRT using kilovoltage cone-beam computed tomography (kVCBCT). kVCBCT datasets were registered to the planning dataset, recontoured and the original plan recalculated on the kVCBCTs to recreate anatomical conditions during treatment. The imaging, structure and dose data were imported into in-house software for the assessment of geometric variation and cumulative equivalent uniform dose (EUD) in the two groups.

Results

The difference in location (ΔCOV) for the bladder between planning and each CBCT was similar for each group. The range of mean ΔCOV for the rectum was 0.15–0.58 cm and 0.15–0.59 cm for the non-ERB and ERB groups. For superior-CTV and inferior-CTV the difference between planned and delivered D_95% (mean ± SD) for the non-ERB group was 2.1 ± 6.0 Gy and −0.04 ± 0.20 Gy. While for the ERB group the difference in D_95% was 8.7 ± 12.6 Gy and 0.003 ± 0.104 Gy.

Conclusions

The use of ERBs in the post-prostatectomy setting did improve geometric reproducibility of the target and surrounding normal tissues, however no improvement in dosimetric stability was observed for the margins employed.     

Dosimetric effect of target expansion and setup uncertainty during radiation therapy in pediatric craniopharyngioma

Purpose

Investigate the effect of tumor change and setup uncertainties on target coverage for pediatric craniopharyngioma during RT.

Methods and materials

Fifteen pediatric patients with craniopharyngioma (mean 5.1 years) were included in this study. MRI was performed before and a median of six times during RT to monitor changes in the tumor volume. IMRT plans were created and compared to the CRT plan used for treatment. The role of adaptive therapy based on GTV changes was investigated. Dosimetric effects of interfraction and intrafraction motion were examined.

Results

The mean of the maximal change in the GTV was 28.5% [−20.7% to 82.0%]. For the standard margin IMRT plans, the mean D₉₅ of the base plan on the base target was 53.6 Gy [53.1-54.1]. The mean D₉₅ of the base plans on the adaptive targets was 52.1 Gy [47.9-54.1]. The D₉₅ for the adaptive plan on the adaptive target was 53.8 Gy [53.4-54.3]. A linear regression equation of y=-0.12x , r² = 0.70, was found for the percent change in D₉₅ of the PTV (y) vs. the percent change in the GTV (x). Inter and intrafraction motion did not affect the target coverage for standard and reduced margin plans.

Conclusions

The GTV of pediatric craniopharyngioma patients change size during therapy and adaptive planning is critical for conformal plans; therefore early and regular surveillance imaging is required.     

Simultaneous integrated boost in breast conserving treatment of breast cancer: A dosimetric comparison of helical tomotherapy and three-dimensional conformal radiotherapy

Background and purpose

To evaluate the dosimetry of helical tomotherapy (HT) and three-dimensional conformal radiotherapy (3D-CRT) in breast cancer patients undergoing whole breast radiation with simultaneous integrated boost (SIB) of the tumor bed.

Material and methods

Thirteen patients with breast cancer treated by lumpectomy and requiring whole breast radiotherapy with tumor bed boost were planned using both HT and 3D-CRT using the field-in-field technique. The whole breast and tumor bed were prescribed 50.68 Gy and 64.4 Gy, respectively, in 28 fractions. Dosimetries for both techniques were compared.

Results

Coverage of the whole breast was adequate with both techniques (V_95% = 96.22% vs. 96.25%, with HT and 3D-CRT, respectively; p = 0.64). Adequate tumor bed coverage was also achieved, although it was significantly lower with HT (V_95% = 97.18% vs. 99.72%; p < 0.001). Overdose of the breast volume outside the tumor bed was significantly lower with HT (V_54.23Gy = 12.47% vs. 30.83%; p < 0.001). Ipsilateral lung V_20Gy (6.34% vs. 10.17%; p < 0.001), V_5Gy (16.54% vs. 18.53%; p < 0.05) and mean dose (4.05 Gy vs. 6.36 Gy; p < 0.001) were significantly lower with HT. In patients with left-sided tumors, heart V_30Gy (0.03% vs. 1.14%; p < 0.05) and mean dose (1.35 Gy vs. 2.22 Gy; p < 0.01) were significantly lower with HT, but not V_5Gy. Contralateral breast V_5Gy (0.27% vs. 0.00%; p < 0.01) and maximum dose were significantly increased with HT.

Conclusions

In breast cancer treated with SIB, both HT and 3D-CRT provided adequate target volume coverage and low heart doses. Tumor bed coverage was slightly lower with HT, but HT avoided unnecessary breast overdosage while improving ipsilateral lung dosimetry.     

Intensity modulated radiotherapy in the management of sacral chordoma in primary versus recurrent disease

Purpose

To investigate treatment outcome in patients suffering from sacral chordoma after intensity modulated radiotherapy (IMRT) for primary versus recurrent disease.

Material/methods

We report on 34 patients with histologically proven sacral chordoma. Seventeen patients were treated at time of initial diagnosis with post-operative IMRT (n = 13) or with IMRT alone (n = 4). Seventeen patients were treated in recurrent disease after surgery (n = 11) or with radiotherapy alone (n = 6). Median total dose to the boost volume (PTV2) was 66 Gy (range, 72-54) with 2 Gy per fraction using an integrated boost concept. Median dose to target volume (PTV1) was 54 Gy in 1.8 Gy.

Results

Local control was 35% (12/34) and overall survival 74% (25/34) after a median follow-up of 4.5 years. Actuarial local control was 79%, 55% and 27% after 1, 2 and 5 years, respectively. Local control was significantly higher in patients treated for primary tumors (p < 0.03) and in total doses >60 Gy (p < 0.01). Actuarial overall survival was 97%, 91% and 70% after 1, 2 and 5 years, respectively.

Conclusion

These data demonstrate that local control after IMRT is higher in patients treated for primary tumors and using higher radiation doses. Therefore, we recommend radiotherapy as part of initial treatment in sacral chordoma.     

Rotational radiotherapy for prostate cancer in clinical practice

Background and purpose

Radiotherapy is the standard treatment in locally advanced prostate cancer. The latest technological improvement is modulated rotational radiotherapy, where one single rotation of the treatment machine is used to conform the dose delivery to the target and spare organs at risk, requiring less than 2 min of beam-on time per treatment fraction.

Materials and methods

We report herein our experience from the first 46 patients treated for prostate cancer, clinical stage T1-3 with rotational therapy (“RapidArc®”, Varian Medical systems) (RA). This patient group is compared to a group of 50 patients treated with a 5-field Intensity Modulated Radiation Therapy (IMRT) technique over the same period. The comparison parameters include target coverage, dose to OAR, treatment time and number of monitor units. Daily-IGRT using implanted gold markers is used before and after treatment to investigate intra-fractional prostate displacement.

Results

RA results in improved sparing of the rectum and achieves desired dose distributions with fewer monitor units and a shorter treatment time (<1.5 min versus up to 8.9 min with IMRT). This shorter treatment time also translates in a decreased risk of patient motion during treatment: daily-IGRT demonstrates reduced prostate motion (<3 mm 3D vector) from 16.7% to 4.7% in RA patients. Only slight side-effects were seen in the two groups of patients.

Conclusions

RA results in improved sparing of the rectum, however, at the expense of an increase in dose to the femoral heads in prostate patients. The treatment time is significantly reduced from 4.9 min on average with 5-field IMRT to 1.1 min with RA, which allows for a reduction of infractional prostate motion.